Persons with certain respiratory conditions receive therapeutic benefits from having supplemental oxygen delivered to their respiratory passages while breathing air from the atmosphere. This supplemental oxygen serves to increase the amount of oxygen delivered to the patient's body tissue through the blood stream. This is accomplished because the supplemental oxygen increases the patient's SaO.sub.2 level which is the measure of oxygen saturated hemoglobin in the blood.
The conventional approach to providing supplemental oxygen to a patient is schematically shown in FIG. 1. This prior art system generally designated 10, includes a supply of oxygen 12. In the embodiment shown, the supply is a portable oxygen supply such as a pressurized oxygen bottle. A flow rate controlling regulator 14 is positioned on the supply 12 and is in fluid communication therewith. Regulator 14 may be a pressure compensated regulator of the type known in the prior art which includes an adjustment member 16 thereon. Adjustment member 16 is adjustable to change the rate of flow from the supply into an oxygen delivery line 18. Oxygen delivery line 18 is in fluid communication with a cannula 20. Cannula 20 includes a pair of passages 22 each of which communicates with a nasal passage 24 of a patient which is shown in phantom.
In conventional oxygen therapy the physiological characteristics of the patient are studied to determine a continuous flow rate of supplemental oxygen that proves beneficial to the patient. Regulator 14 is set to deliver this prescribed flow rate by positioning adjustment member 16. The oxygen is continuously delivered at this prescribed flow rate through the cannula 20 to the patient's nasal passages.
A drawback associated with conventional oxygen therapy is that the patient only benefits from the supplemental oxygen during times in the respiratory cycle when the patient is inhaling in a manner which enables the supplemental oxygen to reach the lungs. At other times the supplemental oxygen delivered is of no benefit, and is lost.
Continuous delivery of oxygen presents a drawback when the patient is using a portable oxygen supply with a limited capacity. When oxygen is delivered continuously the time period the patient may use the portable oxygen supply is limited to the capacity of the supply divided by the prescribed flow rate. The capacity available from a reasonably sized oxygen bottle or other supply may not enable a patient to use a single portable supply for as long as would be desirable.
Others have previously developed oxygen conserving devices to extend the time that a patient may receive oxygen before depleting a supply. These prior approaches generally have drawbacks.
Certain oxygen conserving devices attempt to deliver a fixed pulse of oxygen to a patient at the start of inspiration in each respiratory cycle. However, as a patient's activity level increases, the fixed pulse of oxygen may be insufficient to maintain the patient's blood oxygen level. The patient may have a tendency to desaturate, meaning that their SaO.sub.2 level falls below a patient's required oxygen saturation level.
As a patient's exertion level changes, breathing patterns may also change. Prior oxygen conserving devices rely for their beneficial affect on detecting the beginning of a patient's inhalation or inspiration during each respiratory cycle. Because breathing patterns can become irregular, prior devices often fail to properly detect the optimum point in the respiratory cycle for the delivery of the supplemental oxygen. This can result in desaturation of the patient's blood oxygen level because oxygen is being delivered at inappropriate times. Often during irregular breathing prior devices deliver pulses of oxygen at a frequency that is much higher than the actual breathing rate of the patient. Much of the supplemental oxygen can be wasted when the breathing pattern becomes irregular.
Certain previously developed supplemental oxygen delivery devices deliver a burst of oxygen into a patient's nasal passages when a patient begins to inhale. This burst of oxygen is often uncomfortable for the patient. In addition, such high flow pulses generally cannot be tailored to the patient's physiological requirements or dynamically adjusted to meet the needs of the patient's changing activity level or breathing pattern.
Thus, there exists a need for a supplemental oxygen delivery apparatus and method that conserves oxygen while providing the patient with a therapeutic equivalent of continuous oxygen flow, and which overcomes the drawbacks associated with prior conserving devices.